Gas odorisation is accordingly understood to be the addition of strong-smelling substances (odorants) acting as warning or alarm substances to gases which do not themselves have a significant characteristic odour, i.e. to otherwise substantially or entirely odourless (fuel) gases.
These odorants are perceptible even when highly diluted and because of their exceptionally unpleasant odour they provoke an alarm association in people in the desired way. The odorant must not only have an unpleasant and unmistakable odour but above all must clearly represent a warning odour. The smell of the odorant and the odorised (fuel) gas must therefore not be familiar to people from everyday life, e.g. from the kitchen or home.
Various odorants for fuel gases in general and/or hydrogen in particular have already been described.
In JP-A 55-104393 it is stated that odorants containing an alkyne and at least two compounds chosen from a group comprising methyl acrylate, ethyl acrylate, methyl methacrylate, allyl methacrylate, ethyl propionate, methyl n-butyrate, methyl isobutyrate and phenyl acrylate, and optionally tert-butyl mercaptan, are suitable for the odorisation of fuel gases.
Odorants for fuel gases consisting of ethyl acrylate (70 wt. %) and tert-butyl mercaptan (30 wt. %) are known from JP-B 51-021402.
Mixtures of C4-C7-aldehydes and sulfur compounds are described as odorants in JP-A 50-126004. Odorisation of 1 kg of propane was performed with 50 mg of a mixture of 60 wt. % of valeraldehyde and 40 wt. % of n-butyl mercaptan. Valeraldehyde intensifies the odour of n-butyl mercaptan here. 2-Methyl valeraldehyde was used in a similar way.
In DE-A 19837066 the problem of the sulfur-free gas odorisation of natural gas was solved with mixtures containing at least one acrylic acid C1-C12-alkyl ester and an alkyl-substituted 1,4-pyrazine.
US 2004/0197919 concerns the odorisation of fuels, such as hydrogen for example, for fuel cells for the purposes of leak detection. A large number of organic substances from the compound classes comprising aldehydes, ketones, esters, furanones and pyrazines are proposed. Explicitly cited esters are methyl acetate, butyl acetate, ethyl butyrate, methyl butyrate and ethyl-2-methyl butyrate.
DE 103 00 556 (corresponding to US 2003/0126796) proposes fatty acids such as acetic acid or butanoic acid as odorants for fuel gas for a fuel cell. In US 2004/0072050 a fuel cell system for odorised hydrogen is described wherein butyric acid is cited as the odorant.
JP 2002-060766 describes odorants for fuel gases for a fuel cell wherein hydrogen is not cited as the fuel gas. Odorants based on alkyl esters of C4-C6-carboxylic acids, which preferably contain one or two further substances from the class of mercaptans, sulfides and pyrazides to intensity the olfactory effect, are proposed there.
JP 2003-155488 lists a very large number of odiferous compounds, some of them containing nitrogen and/or sulfur, as odorants for hydrogen, which were examined with regard to the membrane and catalyst compatibility. Methyl acrylate, ethyl acrylate, acetophenone, propanal and butanal are cited among others. Mixtures are not described. A large number of typical odiferous substances are listed, such as e.g. vanillin, benzaldehyde, limonene or 1,8-cineol (eucalyptol), which have no alarm effect, so no reference to particularly suitable or improved odorants in terms of olfactory properties can be taken from this document.
US 2004/0031314 concerns a selection procedure for odorants for the odorisation of hydrogen. Ethyl acrylate is cited, but not classed as an advantageous candidate. Amines such as methylamine, thiols such as ethyl mercaptan or selenium compounds such as ethyl selenol are regarded as being preferred there.
It is known from U.S. Pat. No. 2,430,050 and DE-A 198 37 066 that antioxidants, particularly phenol derivatives, are suitable for stabilising gas odorants containing alkyl acrylate.